The present invention relates in general to regulating circuits, and more particularly, to a current source regulator for providing a predetermined output current proportional to absolute temperature and including an enable input whereby the current regulator may be disabled.
Current regulators are common in modern electronic circuits wherein a source of predetermined current independent of load and power supply voltage is required. A conventional current regulator may comprise a plurality of PNP transistors each conducting the same current flowing through an NPN transistor current mirror, the latter having a predetermined current ratio. The output impedance at the collectors of the PNP transistors is made very large such that changes in the load impedance are negligible. The conventional current regulator may also include an enable input at which an enable signal is applied for disabling the NPN current mirror and, accordingly, the output current. Although the conventional current regulating circuit may take many forms, most if not all of these are sensitive to variation of the enable signal and the inconsistency in the NPN current mirror ratio, both of which contribute to inaccuracy in the output current. The conventional regulator may also include a feedback loop for improving the regulation of the output current; however, this often involves adding considerable complexity to the design possibly limiting the bandwidth of the loop response to changes in the load and power supply voltage. In addition, such complex regulation loops often require excessive compensation for achieving an adequate phase margin to maintain stability.
Hence, there is a need for a simple current source regulator for providing a predetermined output current responsive to an enable signal for disabling the output current flow wherein the output current is invariant to both the enable signal and load.